The present invention relates to rotary regenerative air preheater and more particularly to bypass seals for rotary regenerative air preheaters.
A rotary regenerative air preheater transfers sensible heat from the flue gas leaving a boiler to the entering combustion air through regenerative heat transfer surface in a rotor which turns continuously through the gas and air streams. The rotor is supported in a housing and is divided into compartments by a number of radially extending plates referred to as diaphragms. These compartments are adapted to hold modular baskets in which the heat transfer surface is contained. In the normal arrangement, circumferential bypass seals are provided between the rotor and the housing to prevent the air and gas from flowing around the outside of the rotor.
In conventional air preheaters, the bypass seals have two, separate, overlapping leaves, a base leaf and a second, overlapping leaf which covers leakage paths through the base leaf. Each of the leaves is typically thirty six (36) inches long and there is fifty percent (50%) overlap between the leaves, providing a combined bypass seal length of fifty four (54) inches. The bypass seals are installed in the field, requiring the installer to hold the two seal leaves in place during the installation process.
The present invention involves an improved design of bypass seals for a rotary regenerative air preheater. The invention involves the use of primary and secondary seal leaves that are joined at a single position longitudinally intermediate their first and second ends to form a bypass seal. The first end portion of the primary seal leaf extends longitudinally beyond the first end of the secondary seal leaf and the second end portion of the secondary seal leaf extends longitudinally beyond the second end of the primary seal leaf such that the first end of the primary seal leaf defines the first end of the bypass seal and the second end of the secondary seal leaf defines the second end of the bypass seal. When installed in the air preheater, the first end portion of the primary seal leaf of each bypass seal in one of the seal rings overlaps the second end portion of the secondary seal leaf of an adjacent bypass seal in the seal ring.
Each of the seal leaves includes a base portion and a sealing portion extending from the base portion to a sealing edge. The sealing portion has a plurality of tabs separated by equidistantly spaced slots extending laterally from the sealing edge. The slots provide additional flexibility to the bypass seal and facilitate bending the bypass seal into an arcuate form during installation. One of the tabs of each seal leaf overlaps each of the slots of the other seal leaf to prevent leakage through the slot.
The base portions of each of the seal leaves define a plurality of complimentary equidistantly, longitudinally spaced mounting slots. The first of the mounting slots is positioned at a distance D1 from the first end of the bypass seal and the last of the mounting slots is positioned at the distance D1 from the second end of the bypass seal. The first mounting slot of the primary seal leaf is positioned at the distance D1 from the first end of the primary seal leaf, the last mounting slot of the primary seal leaf is positioned at a distance D2 from the second end of the primary seal leaf, the first mounting slot of the secondary seal leaf is positioned at a distance D2 from the first end of the secondary seal leaf, and the last mounting slot of the secondary seal leaf is positioned at the distance D1 from the second end of the secondary seal leaf, where D2 greater than D1.